{"id":606976,"date":"2026-04-16T01:53:09","date_gmt":"2026-04-16T01:53:09","guid":{"rendered":"https:\/\/www.newsbeep.com\/ca\/606976\/"},"modified":"2026-04-16T01:53:09","modified_gmt":"2026-04-16T01:53:09","slug":"scientists-test-a-fundamental-rule-of-gravity-on-cosmic-scales-and-it-holds-up","status":"publish","type":"post","link":"https:\/\/www.newsbeep.com\/ca\/606976\/","title":{"rendered":"Scientists test a fundamental rule of gravity on cosmic scales \u2014 and it holds up"},"content":{"rendered":"

For more than 300 years, Isaac Newton\u2019s simple rule about gravity has held up: the farther apart two objects are, the weaker their pull on each other. It works for apples. It works for planets.<\/p>\n

Now, scientists have put that same rule to the test on a scale Newton could never have imagined \u2014 across hundreds of millions of light-years, where entire clusters of galaxies drift through space.<\/p>\n

A new study<\/a> in Physical Review Letters finds that gravity still behaves as expected even at those distances. And that result strengthens the case for something scientists still can\u2019t see directly: dark matter.<\/p>\n

\u201cThis is really a test of a basic question,\u201d said Kris Pardo<\/a>, co-author of the study and assistant professor of physics and astronomy<\/a> at the USC Dornsife College of Letters, Arts and Sciences. \u201cIf you look at how galaxy clusters fall toward each other, does it match what our current theory of gravity predicts?\u201d<\/p>\n

The answer, according to the study, is yes.<\/p>\n

Scientists watch galaxies fall to test gravity<\/p>\n

To test gravity on such enormous scales, researchers needed a clever workaround. You can\u2019t exactly drop two galaxy clusters and watch what happens.<\/p>\n

Instead, the team measured how large numbers of clusters of galaxies move toward one another over time in a kind of cosmic dance driven by gravity.<\/p>\n

They used data from the Atacama Cosmology Telescope in Chile, which observes faint radiation left over from the Big Bang known as the cosmic microwave background<\/a>. When galaxy clusters move, they leave tiny imprints in this ancient light.<\/p>\n

\"ShadesResearch by the Atacama Cosmology Telescope collaboration has led to the most precise images yet of the cosmic microwave background radiation that was visible only 380,000 years after the Big Bang. (Image source: ACT Collaboration; ESA\/Planck Collaboration.)<\/p>\n

Despite this phenomenon\u2019s long name \u2014 the kinematic Sunyaev-Zeldovich effect \u2014 the idea is simple: Moving galaxy clusters slightly nudge this background radiation in a way that reveals how fast the clusters are traveling.<\/p>\n

The researchers combined those velocity measurements with a massive map of galaxy positions. By comparing where clusters are and how they move, the team could estimate how strongly gravity is pulling them together.<\/p>\n

\u201cWe\u2019re basically asking, given where all this matter is, how fast should things be moving if gravity works the way we think it does?\u201d Pardo said. \u201cAnd then we check that against what we actually see.\u201d<\/p>\n

Newton\u2019s rule holds up on cosmic scales<\/p>\n

The researchers found that gravity indeed does appear to weaken with distance almost exactly as Newton predicted.<\/p>\n

\u201cWe found that galaxy clusters fall toward each other in a way that\u2019s consistent with our standard model of the universe,\u201d Pardo said.<\/p>\n

That might sound unsurprising, but testing gravity\u2019s basic rule on such vast scales has been difficult, and some scientists have proposed alternatives.<\/p>\n

One idea, known as Modified Newtonian Dynamics, or MOND, suggests that gravity behaves differently at very large distances. If so, dark matter \u2014 the mysterious, invisible substance thought to make up most of the universe\u2019s matter \u2014 might not be needed to explain how galaxies move.<\/p>\n

The new study puts MOND under pressure on these scales. \u201cWe were able to essentially rule out one popular alternative in this analysis,\u201d Pardo said. \u201cThis is a particularly clean test because it looks at how things are moving right now, not just how structure formed over time.\u201d<\/p>\n

Gravity study makes a case for dark matter
\n\"LinesThis sketch shows paths of light from a distant galaxy that is being gravitationally lensed by a foreground cluster. (Image source: NASA; ESA.)<\/p>\n

The findings also speak to one of the biggest open questions in physics: What is the universe made of?<\/p>\n

If gravity behaves as expected on these vast scales, then the motions of galaxies and galaxy clusters are still best explained by extra mass \u2014 mass we can\u2019t see.<\/p>\n

\u201cOur results suggest that the standard theory of gravity works really well,\u201d said Patricio Gallardo, a research associate at the University of Pennsylvania and lead author of the study. \u201cIf that\u2019s the case, then we do need dark matter to explain the rotations of galaxies and the movements of galaxies within clusters.\u201d<\/p>\n

In other words, the study doesn\u2019t detect dark matter directly. But by narrowing the alternatives, it strengthens the argument that something unseen is out there.<\/p>\n

Gallardo says he was surprised just how well the basic rule still holds up. \u201cIt\u2019s kind of amazing. Newton was thinking about planets in the solar system. And now we\u2019re testing the same rule on galaxy clusters separated by hundreds of millions of light-years \u2014 and it still works.\u201d<\/p>\n

Why the scale matters \u2014 and what\u2019s next<\/p>\n

The study, one of the largest-scale direct tests of gravity to date, probes distances far beyond anything previously measured in this way.<\/p>\n

That scale matters because scientists want to know whether the laws of physics are truly universal \u2014 the same everywhere, from Earth to the farthest reaches of space. So far, the results suggest they are.<\/p>\n

The work also opens the door to even more precise tests. Upcoming surveys and telescopes are expected to collect far more data, allowing researchers to push these measurements further.<\/p>\n

\u201cWith better data, we can start looking for even tiny deviations,\u201d Gallardo said. \u201cIf there\u2019s any new physics hiding out there, this is one way we might find it.\u201d<\/p>\n

What this test can\u2019t answer yet<\/p>\n

The test probes enormous distances, but it doesn\u2019t cover every scale or environment in the universe. Also, the signal the researchers measured is extremely subtle, and the analysis depends on combining data from hundreds of thousands of galaxies. That means the results rely on statistical methods and high quality probes of galaxies and the cosmic microwave background.<\/p>\n

\u201cThere are some technical limitations, especially when applying this to alternative theories like MOND,\u201d Pardo said. \u201cBut overall, this is a pretty clean test.\u201d<\/p>\n

Gallardo added that the precision of the measurement, which is still limited by the amount of available data, should improve.<\/p>\n

\u201cAs we get larger galaxy samples and better observations, we\u2019ll be able to tighten these constraints,\u201d he said.<\/p>\n

For now, the takeaway is simple: Across vast distances, gravity still seems to follow the same basic rule first written down in the 1600s \u2014 quietly guiding galaxy clusters, just as it guides falling apples.<\/p>\n","protected":false},"excerpt":{"rendered":"For more than 300 years, Isaac Newton\u2019s simple rule about gravity has held up: the farther apart two…\n","protected":false},"author":2,"featured_media":606977,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[7],"tags":[49,48,15846,229098,994,66],"class_list":{"0":"post-606976","1":"post","2":"type-post","3":"status-publish","4":"format-standard","5":"has-post-thumbnail","7":"category-science","8":"tag-ca","9":"tag-canada","10":"tag-physical-sciences","11":"tag-physics-and-astronomy","12":"tag-research","13":"tag-science"},"_links":{"self":[{"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/posts\/606976","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/comments?post=606976"}],"version-history":[{"count":0,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/posts\/606976\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/media\/606977"}],"wp:attachment":[{"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/media?parent=606976"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/categories?post=606976"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/tags?post=606976"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}